The present invention relates to an oxygen absorbent packet employing a double packaging material.
The use of oxygen absorbents for the preservation of food products and other items has recently grown increasingly common. Oxygen absorbents typically consist primarily of a metal powder, such as iron, organic compounds such as hydroquinone, catechol, and ascorbic acid, or reducing sulfur compounds such as sulfites and dithionites. They are normally used in packet form with the absorbent enclosed in an air-permeable packaging material. The oxygen-absorbing properties of an oxygen absorbent vary with the properties of the main component, such as iron, but the properties of the packaging material in which the absorbent is enclosed also have a substantial effect on the performance of the oxygen absorbent. In particular, the oxygen absorption rate is primarily a function of the gas permeability of the packaging material. Moreover, when an oxygen absorbent is used with high-moisture food products, the transfer of moisture between the food and the oxygen absorbent has a very significant effect on the performance of the absorbent. The degree and manner in which this transfer of moisture takes place is to a large extent determined by the construction of the packaging material.
A laminate of paper and perforated polyethylene film has hitherto been used as the packaging material for oxygen absorbents. However, when an oxygen absorbent packet made with this type of packaging material is used to help preserve a food product with a high moisture content, the packaging material becomes damp because of the paper's lack of resistance to water, resulting in the staining of the oxygen absorbent packet.
Another drawback of this type of packaging material is that deformation of the holes present to provide gas-permeability may occur during heat-sealing, resulting in at least a partial loss of air-permeability and/or leakage or oozing out of the packet contents, marring the appearance of the packet. Under such circumstances, it has been impossible to raise the oxygen absorption rate by increasing the number or size of the holes. Yet another significant problem is the threat to safety and hygiene posed by the leakage of the packet contents (oxygen absorbent) through the packaging material.
Japanese Patent Publication (Kokai) No. 51096/78 discloses a method for perforating two plastic films having different melting points, then placing one film over the other (or sandwiching a sheet of paper between the two) and bonding the layers together to form a laminated packaging material for an oxygen absorbent. However, in this method the heat-sealing process can cause the holes to become deformed or even closed. Accordingly, the controlled production of packaging material having the uniform, desired level of air-permeability is very difficult.
Another problem is that the gas-permeability varies depending on how well each of the films and the paper are bonded to each other in the bonding process. Japanese Patent Publications (Kokai) Nos. 124440/1981 and 124441/1981 disclose similar inventions in which the same problem arises. Here too, the gas-permeability varies a great deal depending on the bonding conditions during lamination. Other areas of concern include the influence of the adhesive used on the air-permeability and the safety and health problems associated with adhesive use.
The inventors conducted careful studies in an attempt to develop an oxygen absorbent packet that uses a packaging material the external appearance of which is not marred even when employed to preserve foods with a high moisture content, and which material, in addition, is hygienically safe and provides good control of gas-(or air-)permeability at the desired level in a uniform, reproducible manner. As a result of these efforts, the inventors ultimately arrived at the present invention.